The invention is generally directed to pigments, such as toner pigments, and, more specifically, to processes for the preparation thereof. In embodiments the present invention relates to toner and carrier particles with fluorinated, especially fluorosilanated pigments, such as fluorinated carbon blacks obtained, for example, by solution or gas phase methods. The pigments obtained with the processes of the present invention can be selected as a component for carrier coatings, or as a toner component. Although it is not desired to be limited by theory, it is believed that the fluorination passivates the pigment. The fluorinated pigments obtained with the process of the present invention possess a number of important characteristics, such as increased negative charging, compared to the untreated pigment. Thus, the pigments, such as for example the fluorosilanated carbon black, that result from the treatment process have about -0.1 to about -1.0 volt more negative contact potential than the corresponding untreated pigments. In applications, such as for toner or carriers, where these treated pigments are used in carrier coatings or in toners the negative charging of the carrier or toner can be increased by 5 to 30 microcoulombs per gram compared to the carrier or toner with untreated pigments. The charging level, as determined by the contact potential, or by the toner or carrier charge, can be selected by controlling the fluorosilane content of the fluorosilanated pigment, whereby the charge level of the fluorosilanated pigment becomes increasingly more negative as the amount of fluorosilane on the pigment increases, and as the length of the fluorosilane chain increases. The fluorosilane concentration can be varied, from about 5 weight percent of the pigment to about 90 weight percent of the pigment, and the length of the fluorosilane chain can be varied to contain from 1 carbon atom to about 30 carbon atoms. Thus, when the toner resin is changed, when toner additives are added, such as waxes, when the pigment is changed, or when the carrier composition is changed with the fluorosilanation process it is possible to vary the pigment treatment, which enables the overall charge to remain constant. With toners that incorporate different pigments, it is possible to fluorosilanate all of the pigments, and also by varying the fluorosilane treatment, all of the resulting toners with the different pigments will have the same or similar toner charge. This enables very simple construction of the electrophotographic or xerographic apparatus that makes use of more than one toner color. The charge can be varied without affecting the conductivity of the pigment, or charge control agent particles. This is important for maintaining high conductivity in the coated carrier. This is also important with toner additives, such as charge control agents, where the conductivity of the additive must be maintained. There is also the advantage with the present invention that there is no change in other important properties of the pigment, such as color, particle size or the conductivity of the pigment particle. Further, since the fluorine does not react with the pigment, the fluorination process can be applied to conductive or nonconductive particles, color or black pigments, doped tin oxide, metal particle, wax, charge control agent particles, or toner particles. Since the pigment treatment is accomplished at temperatures that are close to room temperature, there is no degradation of the pigment due to high temperatures. The pigment that is selected may be one that is unstable at elevated temperatures, that is above room temperature. For example, X-copper phthalocyanine pigment listed in the Color Index as CI 74160 is only stable to about 150.degree. C. for 30 minutes, while a monoazo pigment identified in the Color Index as CI 12700, CI Solvent Yellow 16, decomposes at temperatures of 100.degree. C.
For carrier particles, the fluorosilanated pigment, such as carbon black, has the advantage that the charge of the carrier can be varied by 5 to 30 microcoulombs per gram of toner particles by varying the fluorosilanation treatment of the pigment, whereby the charge level of the fluorosilanated pigment becomes increasingly more negative as the amount of fluorosilane on the pigment increases, and as the length of the fluorosilane chain increases, and charge can be varied without any variation in the conductivity of the carbon black. It is an important property of the carrier to have a specific conductivity that is determined by the specific xerographic or electrophotographic process in which the carrier is utilized to effectively function in that process, and wherein the conductivity of the carrier is determined by the carbon black and by the amount of the carbon black incorporated into the carrier coating, and to provide to the toner a specific charge level, typically of between about 10 and about 40 microcoulombs per gram of toner. It is also desirable to enable varying the charging level of the carbon black to accommodate any changes in the toner properties without any change in the carrier conductivity, which would reduce the function of the combination of carrier and toner as, for example, resulting in long charging times of greater than about 5 minutes.
For toner particles, the fluorosilanated carbon black has the advantage that the charge of the toner can be varied by 5 to 30 microcoulombs per gram, as measured by the known Faraday Cage blow-off tribo method. The fluorosilanation treatment can be varied as indicated herein, whereby the charge level of the fluorosilanated pigment becomes increasingly more negative as the amount of fluorosilane on the pigment increases, and as the length of the fluorosilane chain increases, and the toner charge can be varied without any variation in the conductivity of the carbon black. The conductivity of the toner is primarily determined by the pigment, such as carbon black, and by the amount of the carbon black incorporated into the toner. With the present invention, there is enabled in embodiments a variation in or preselection of the charging level of the carbon black to accommodate any changes in the other components of the toner, such as for example wax, changes in the composition of the toner resin, or to accommodate changes in the carrier composition without any change in the toner conductivity, which would reduce the function of the combination of carrier and toner as, for example, resulting in long charging times of greater than about 5 minutes, or in broad charge distributions, as when the width of the distribution of toner charge is approximately equal to or greater than the absolute magnitude of the average charge.
In the prior art as illustrated in U.S. Pat. No. 4,524,119, the fluorination occurs at high temperatures, 150 to 600.degree. C., in the gas phase, and involves a reaction of the elemental fluorine with reactive bonds of the carbon black. This fluorination is applied to the entire bulk of the sample, changing the properties of the carbon black itself. As indicated in this patent, the fluorination changes the charging level, and increases the resistivity of the carbon black. Thus, it is not believed possible to separately change the charge and the conductivity since the fluorine reacts with the carbon black, and the process is substantially different for each carbon black. This prior art is only applicable, it is believed, to conductive particles that have reactive bonds, and thus can be used with carbon black, but could not be used with other conductive particles, such as doped tin oxide metal particles. Furthermore, the fluorination treatment of the above prior art is accomplished at elevated temperatures which would decompose or degrade many materials like color pigments, organic charge control agents, and toner particles, disadvantages avoided or minimized with the present invention. Also, because of the very reactive nature of the prior art process, the color of the pigment would change. For example, pigments, such as diazo dyes identified in the Color Index as CI 26050, are unstable at high temperatures; CI Solvent Red 19 is only stable to about 100.degree. C.; X-copper phthalocyanine pigment listed in the Color Index as CI 74160 is only stable to about 150.degree. C. for 30 minutes; and CI Solvent Yellow 16, decomposes at temperatures of 100.degree. C. When a charge control additive component or CCA particle is to be treated, it is usually necessary to retain the particle intact to prevent or minimize agglomeration. Thus, it is necessary to retain the temperature of the treatment process below the melting temperature of the CCA. Thus, cetylpyridinium chloride, for example, melts at about 85.degree. C. When a toner particle is to be treated, it is usually necessary to retain the toner particles intact to prevent or minimize agglomeration. Thus, it is important to retain the temperature of the treatment process below the flowing temperature of the toner, which is usually about or below the toner glass transition temperature, which is generally between about 40.degree. C. and about 65.degree. C. With the fluorosilane product and treatment of the present invention, treatment is near or at room temperature in embodiment, and thus no degradation, melting, or flow of pigments, CCAs or toner particles results. The above mentioned pigments, toners, and charge control agents are incompatible with the processes of the prior art U.S. Pat. No. 4,524,119, which require higher temperatures of 150 to 600.degree. C., which would be above the stable temperature for these materials.
Other patents illustrating the preparation of fluorinated carbon, include U.S. Pat. Nos. 2,786,874, 3,925,592; 3,925,263; 3,872,032; and 4,247,608.
To attain negative charging in a carrier or toner would normally require adding an additional component to the carrier (toner), or even changing the resin. A much simpler and more economical design approach developed after extensive research is to fluorosilanate one (or more) existing materials, thereby achieving the desired charging properties without having to make carrier or toner design changes. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
Toner pigments and coated carriers with carbon black polymer mixtures are known, reference for example U.S. Pat. No. 4,221,856, which discloses electrophotographic toners containing carbon black and resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, and each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens, such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a division of U.S. Pat. No. 4,291,111; and similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens.
Also, there are disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition and which toner contains pigments like carbon black, cyan, magenta, yellow, and mixtures thereof. Further, there are illustrated in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with resin particles and pigment particles like carbon black, and as charge enhancing additives alkyl pyridinium compounds. Additionally, other documents disclosing positively charged toner compositions containing resin and pigment like carbon black, and which toners also contain charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 4,394,430, and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive.
U.S. Pat. No. 5,278,016 discloses the preparation of halogenated toner particles. The halogen changes the chemical nature of the surface layer of the toner particles. The preparation of the halogenated surface layer depends on the presence of certain reactive groups on the toner particle surface, which react in the presence of the halogenating agent. This process is applicable to toners, or other materials, with such surface groups present. If the material to be treated by this process, do not have the reactive group present, then the halogen does not become affixed to the surface of the material, and sufficient halogen may not be present on the material after the treatment to provide substantial change in the charging of the material. The halogenation process of the prior art does not result in a general increase in negative charging of the toner surface after reaction with the halogenating agent, but does show a general reduction in charging ability of the toner, whether it is in a negative or positive charging developer. Thus, Table I of U.S. Pat. No. 5,278,016 shows a reduction in negative toner charging of 20 to 30 microcoulombs per gram in two toners, while Table II generally shows a reduction of positive charging from about 5 to about 20 microcoulombs per gram of toner, for the toner examples described therein, while only in one toner shown in Table II is there an example of a small increase of about 4 microcoulombs per gram of toner in positive charging.
Illustrated in U.S. Pat. No. 5,484,675, the disclosure of which is totally incorporated herein by reference, is a toner composition comprised of resin and pigment particles where the pigment particles are treated with a flurosilane polymer.
While toner pigments are known, there is a need for new pigments with many of the advantages illustrated herein. More specifically, there is a need for novel halosilanated, especially fluorosilanated pigments, which can be selected as toner pigments and as a component of carrier coatings, and wherein the resulting compositions permit excellent xerographic characteristics, including high negative charge, triboelectric stability, relative humidity insensitivity, and the like. There is also a need for economical and direct processes for the preparation of fluorosilanated pigments, especially fluorosilanated carbons. These and other needs are achievable with embodiments of the present invention.